Electric Work Vehicle, Battery Pack for Electric Work Vehicle and Contactless Charging System

ABSTRACT

An electric work vehicle includes: a battery pack that is arranged between a left rear wheel arranged outside of a left frame and a right rear wheel arranged outside of a right frame, the front end of the battery pack being located forward of an axle center of a rear wheel unit; a left motor that is arranged above the battery pack, in the periphery of the left rear wheel, receives a supply of power from the battery pack, and transmits rotational power to the left rear wheel; and a right motor that is arranged above the battery pack, in the periphery of the right rear wheel, receives a supply of power from the battery pack, and transmits rotational power to the right rear wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application Nos.2015-224090 and 2015-224091, both filed Nov. 16, 2015, and JapanesePatent Application No. 2016-065374 filed Mar. 29, 2016, the disclosuresof which are hereby incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electric work vehicle such as anelectric mower, a battery pack for an electric work vehicle, and acontactless charging system.

Description of Related Art

First Related Art

In the field of passenger vehicles, electric vehicles that travel usingthe rotational force of an electric motor have started to becomewidespread. In such a case, a battery is mounted in the vehicle as thepower source of the electric motor. The battery temperature needs to bekept at a suitable temperature in order to maintain the performance ofthe battery, and therefore a cooling structure is often included in thebattery. For example, with a vehicle battery pack disclosed in JP2014-075181 A, a battery cell group, which is multiple battery cells,and a cooling fan that allows air to flow to the battery cell group areaccommodated in a case. In the case, an inlet through which air isguided from the outside into the case, and an outlet through which airis discharged to the outside of the case are formed. Air flow thatoccurs due to the cooling fan being driven so as to rotate passesthrough an air suction flow path that extends in the gaps between thebattery cells and in a bottom portion space between the inner sidebottom surface of the case and the bottom surface of the battery cellgroup. In other words, the cooling air guided from the outside of thevehicle to the inside of the case through the inlet is discharged fromthe outlet to the outside of the case via the air suction flow path, thebottom portion space, and the gaps between the battery cells.Furthermore, multiple heat radiating fins that protrude downward areprovided on the lower surface of the case.

However, in a work vehicle that travels while performing work, as with amower, a rice transplanter, a tractor, or the like, the surroundingenvironment for work travel is worse compared to the surroundingenvironment of an automobile or the like, and if cooling air is taken infrom the surroundings, waste such as cut grass or straw tends to bemixed in with the cooling air, which causes the problem of clogging ofthe cooling air passage.

In view of the foregoing circumstances, there has been demand for abattery pack having a structure that is suitable for an electric workvehicle that performs work travel in a surrounding environment in whichforeign matter such as grass or straw is floating. In such a case, ifmultiple battery modules are included in such a battery pack, it is alsoimportant to make the temperatures of the battery modules as uniform aspossible.

Second Related Art

WO 2013/015171 A1 discloses a lawnmower in which a left and right pairof rear wheels are driven independently by a left and right pair ofmotors. The left and right pair of rear wheels are supported by a rearaxle case extending therebetween. A gear case extends from a centralportion of the rear axle case, perpendicular to the direction in whichthe rear axle case extends, a left-side motor is furthermore equipped onthe left side so as to extend in the vehicle lateral direction from theleading end of the gear case, and a right-side motor is furthermoreequipped on the right side so as to extend in the vehicle lateraldirection from the leading end of the gear case. The rotational power ofthe motors is transmitted to an axle mounted in the rear axle case via apower transmission mechanism mounted in the gear case. As is apparentfrom FIG. 2 of WO 2013/015171 A1, a left and right pair of motors thatextend linearly in the vehicle body lateral direction and a rear axlecase that extends linearly in the vehicle body lateral direction arejoined at respective central portions by a gear case that extends in thevehicle body front-rear direction. Accordingly, the case structure inwhich a mechanism for transmitting the power from the motors to the rearwheels is mounted has a rather complicated shape, and causes an increasein cost. Furthermore, since the left and right pair of motors arearranged inside of the vehicle body frame and the battery is arrangedbetween the left and right pair of motors, there is a problem in that alarge-sized battery cannot be used.

JP 2008-168869 A (or US 2009/0000839 A1 corresponding thereto) disclosesa hybrid lawnmower in which a left motor that drives a left rear wheeland a right motor that drives a right rear wheel are each attached tothe outside of a frame, and an engine and a battery are arranged betweenthe left motor and the right motor. The left motor and the right motorare wheel motors, and the rear wheel axle centers match the motorrotational axis center. With this structure, the engine and the batterypack, which have large weights, are located rearward of the rear wheelaxle center, as a result of which the weight balance regarding the rearwheel axle center deteriorates. However, since the center of gravity ofthe left motor and the right motor is substantially on the rear wheelaxle center, the left motor and the right motor cannot improve thedeterioration of the weight balance.

In view of the foregoing circumstances, there has been demand forimprovement of vehicle body balance and for ensurement of sufficientbattery space in an electric work vehicle including a left motor thatdrives a left rear wheel and a right motor that drives a right rearwheel.

Third Related Art

With a forklift disclosed in JP 2014-082339 A, a primary-sidecontactless power supply pad (primary-side coil) laid on the groundsurface and a secondary-side contactless power supply pad(secondary-side coil) that receives power through electromagneticcoupling are provided between a front wheel and a rear wheel on one sideof the lower surface of the forklift. In the case where a forkliftmechanism serving as a work apparatus attached to a traveling vehiclebody is arranged forward of the front wheels, as with a forklift, thereis relative spatial leeway below the vehicle body between the frontwheels and the rear wheels, and therefore the secondary-side coil can bearranged between the front wheels and the rear wheels. The primary-sidecoil is provided on the ground surface or on a support platform arrangedon the ground surface.

With an electric mower, a mower unit serving as the work apparatusattached to the traveling vehicle body is arranged forward of the rearwheels, and therefore there is little space that can be used freelybelow the vehicle body frame in the region forward of the rear wheels,or in other words, in the region near the ground surface. Also, becausethe weight of the battery pack is large, for the stability of thevehicle body, it is preferable to arrange the battery pack at a lowposition on the vehicle body. Because of this, in a contactless chargingsystem used in an electric work vehicle such as an electric mower,suitable arrangement of the battery pack, the primary-side coil, and thesecondary-side coil is important.

SUMMARY OF THE INVENTION

[1] In order to solve the problem stated in the “First Related Art”, anelectric work vehicle battery pack includes: a sealed battery caseincluding a front case portion and a rear case portion; a horizontalpartitioning wall that divides an interior of the front case portioninto a first space and a second space in a vertical direction, anddivides an interior of the rear case portion into a third space and afourth space in the vertical direction; a battery electric unitaccommodated in one of the first space, the second space, the thirdspace and the fourth space; and a battery module accommodated in each ofthe remaining spaces among the first space, the second space, the thirdspace and the fourth space.

Note that “sealed” above does not mean that the interior space of thebattery case is kept in a completely airtight state, but is used as aterm with a broader meaning that encompasses a loosely airtight state inwhich the flow of outside air to the interior space is suppressed andthe outside air temperature and the temperature of the interior spaceare not easily equalized.

Also, the phrases “first space”, “second space”, “third space”, and“fourth space” do not limit the number of divided spaces to four, andthe battery case may be further divided into a fifth space, a sixthspace, and the like.

In this configuration, the interior of the sealed battery case isdivided into multiple spaces by a horizontal partitioning wall, abattery electric unit is arranged in one space, and battery modules arearranged in the remaining spaces. Thus, waste such as cut grass or strawsubstantially does not enter the interior of the battery case. Also,because the interior of the battery case is divided vertically by thehorizontal partitioning wall, the heat emitted from the multiple batterymodules is prevented from being focused on the roof region of thebattery case.

As a particularly preferable embodiment, a circulation fan configured tocreate a circulated air flow that circulates through the first space,the second space, the third space and the fourth space is included. Inthis configuration, multiple battery modules and a circulation fan areaccommodated in a sealed manner in one battery case, and by circulatingthe air in the case internal space using the circulation fan andsuppressing the entrance of outside air by sealing the battery case, thetemperature of the case internal space is uniformized while foreignmatter from the outside is prevented from entering. In this case, whenthe electric unit and the battery modules are arranged such that thecooling air created by the circulation fan passes through the electricunit and the battery modules in sequence, the temperature distributionof the battery modules can be made as uniform as possible. Accordingly,the temperature distribution of the battery module is easier to makeuniform, and the battery modules electrically operate efficiently.

Note that the scope of the present invention extends also to an electricwork vehicle in which the above-described battery pack is mounted.

[2] In order to solve the problem stated in the “Second Related Art”, anelectric work vehicle that includes a left motor and a right motor thatreceive a supply of power from a battery pack, and that performs travelwork by using the left motor to drive a left rear wheel and using theright motor to drive a right rear wheel includes: a left frame and aright frame that extend in a vehicle body front-rear direction with aninterval therebetween in a vehicle body lateral direction; a rear wheelunit having a left rear wheel arranged outside of the left frame in thevehicle body lateral direction and a right rear wheel arranged outsideof the right frame in the vehicle body lateral direction; a battery packarranged between the left rear wheel and the right rear wheel, a frontend of the battery pack being located forward of an axle center of therear wheel unit in the vehicle body front-rear direction; a left motorthat is arranged above the battery pack in the periphery of the leftrear wheel and is configured to receive a supply of power from thebattery pack and transmit rotational power to the left rear wheel; and aright motor that is arranged above the battery pack in the periphery ofthe right rear wheel and is configured to receive a supply of power fromthe battery pack and transmit rotational power to the right rear wheel.

With this configuration, due to the fact that the front end portion ofthe battery pack is located further forward relative to the rear wheelaxle, the center of gravity of the battery pack does not deviatesignificantly from the rear wheel axle in a side view even if thebattery pack is lengthened and the rear end portion thereof is locatedrearward. Therefore, adverse effects that the weight of the battery packhas on the vehicle body balance of the vehicle body are reduced. Also,by arranging the left motor and the right motor above the battery pack,the space above the battery pack is used effectively, the overall lengthof the vehicle body is suppressed, and an increase in compactness ispossible.

In this case, if the battery pack is arranged such that the center ofgravity of the battery pack is within a rear wheel segment defined bythe left rear wheel and the right rear wheel in the vehicle bodyfront-rear direction and the vehicle body lateral direction in planview, adverse effects that the battery pack has on the stability of thevehicle body can mostly be ignored. The rear wheel segment in thiscontext is a rectangle that is centered about the rear axle center,which is the axle center of the rear wheels, and is obtained by usingthe rear wheel radius as the length of one side in the vehicle bodyfront-rear direction and by using the interval between the left rearwheel and the right rear wheel as the length of the other side. Morepreferably, the center of gravity of the battery pack is located on acenter line in the vehicle body front-rear direction and is within thelength of the radius of the rear wheel from the rear axle center in thevehicle body front-rear direction. Accordingly, the weight of thebattery pack contributes to the stability of the vehicle body.

From the viewpoint of the stability of the vehicle body, it is desirablethat the battery pack, which is a heavy load, is arranged at a lowposition. However, if the above-ground height of the battery pack islow, an inconvenience occurs in which the rear end portion of thebattery pack comes into contact with the ground surface during off-roadtravel or uphill travel.

In order to eliminate this inconvenience and ensure that the center ofgravity of the battery pack is as low as possible, it is desirable tolower the above-ground height of the front portion of the battery packand raise the above-ground height of the rear portion of the batterypack. For this reason, in a preferred embodiment of the presentinvention, the battery pack includes a front-side rectangular cuboidportion and a rear-side rectangular cuboid portion shifted upwardrelative to the front-side rectangular cuboid portion, and is formed asa level-difference three-dimensional shape having level differences onan upper surface and a lower surface of the battery pack between thefront-side rectangular cuboid portion and the rear-side rectangularcuboid portion. In particular, in order to suppress contact with theground surface during off-road travel or uphill travel, it is preferablethat the rear end of the battery pack is located rearward of the rearwheel unit in the vehicle body front-rear direction, and theabove-ground height of the rear end of the battery pack is configured tobe higher than the above-ground height of the rear axle case.

[3] In order to solve the problem stated in the “Third Related Art”, acontactless charging system for an electric work vehicle includes: aprimary coil unit that includes a coil power supply circuit portion anda primary coil arranged above the coil power supply circuit portion, andis arranged on a ground surface; a battery pack arranged at a rearportion of a vehicle body frame, between a left and right pair of rearwheels; a secondary coil that electromagnetically couples with theprimary coil; a charging circuit portion configured to rectify powerfrom the secondary coil and supply the rectified power to the batterypack; and a coil support member for arranging the secondary coil belowthe battery pack.

With this configuration, a primary coil unit having a coil power supplycircuit portion and a primary coil is arranged on a ground surface side,and a secondary coil unit that electromagnetically couples with theprimary coil is attached on the vehicle body side of the electric workvehicle. With the coil support member, the secondary coil is arrangedbelow the battery pack, which is arranged between the left and rightpair of rear wheels in the rear portion of the vehicle body frame. Inorder to avoid contact with an obstacle that exists on the groundsurface during travel, the secondary coil is arranged at a position thatis as high from the ground as possible, and therefore the position ofthe primary coil needs to be made higher. With this configuration, theprimary coil unit has a two-stage structure, the coil power supplycircuit portion being arranged on the lower stage, and the primary coilunit being arranged on the upper stage. Therefore, the primary coil unitis at a high position from the ground surface, which is structurallyconvenient.

The charging circuit portion includes a rectifier through which a largecurrent flows, and has a relatively large shape. Therefore, the chargingcircuit portion requires a wide and stable installation location. Forthis reason, in a preferred embodiment according to the presentinvention, the charging circuit portion is attached to an upper portionof the battery pack. Due to the fact that the outer shape of the batterypack is relatively simple, as with a rectangular cuboid or a combinationof rectangular cuboids, the upper portion of the battery pack isrelatively wide and flat, and therefore the charging circuit portion isstably attached to the upper portion.

Furthermore, in one preferred embodiment of the present invention, arecessed portion is formed at a rear-side lower portion of the batterypack and the secondary coil is arranged in the recessed portion.Accordingly, the surroundings of the secondary coil are at leastpartially protected by the battery pack, which has a high rigidity, andtherefore damage or the like caused by contact with an outside object issuppressed.

If the air pressure of the rear tires fluctuates or if the weight ofadditional freight fluctuates, the above-ground height of the secondarycoil attached to the electric work vehicle side will change, and theinterval between the primary coil and the secondary coil will deviatefrom an optimal value. This adversely affects the charging efficiency,and therefore the interval between the primary coil and the secondarycoil needs to be brought near the optimal value. For this purpose, inone preferred embodiment of the present invention, the primary coil unitis provided with an elevation mechanism configured to raise and lowerthe primary coil. With the elevation mechanism, the above-ground heightof the primary coil can be adjusted, and the interval between theprimary coil and the secondary coil can be set to the optimal value.

In a preferred embodiment of an electric mower in which a contactlesscharging system is incorporated, a mower unit hangs down elevatably at afront portion of the vehicle body frame, and an electric motor unitconfigured to drive the rear wheels using power supplied from thebattery pack via a motor power supply circuit portion is arrangedforward of an axle center of the rear wheels, between the rear wheels.With this configuration, with the mower unit and the electric motorunit, it is possible to solve the problem in which the center of gravityof the vehicle body is located rearward in the vehicle body and thevehicle body balance deteriorates due to the battery pack being arrangedon the rear portion of the vehicle body frame.

Furthermore, in one preferred embodiment of the electric mower, theelectric motor unit includes a left motor that drives one rear wheel viaa left transmission, and a right motor that drives the other rear wheelvia a right transmission, the left motor and the left transmission beingarranged between the one rear wheel and the battery pack, and the rightmotor and the right transmission being arranged between the other rearwheel and the battery pack. With this configuration, stability of thevehicle body and compactness of the travel power transmission system areachieved by consolidating heavy loads such as the electric motor unitand the transmission, which constitute the travel power transmissionsystem, near the axle center of the rear wheel.

The mower unit is near the ground surface during mowing work travel, andis pulled up to its highest position away from the ground duringnon-work travel. The mower unit is located forward in the vehicle bodyrelative to the secondary coil, and therefore fulfills the role of aguard for the secondary coil during travel. For this reason, it ispreferable that the lower surface of the mower unit at the highestposition is set to be lower than the lower surface of the secondarycoil.

Other features and advantages will become apparent upon reading theembodiments described below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a first embodiment (same through to FIG. 9),and is a partially cut-away perspective view showing a basic structureof a battery pack.

FIG. 2 is a side view schematically showing a relationship between thebattery pack mounted in an electric work vehicle and rear wheels.

FIG. 3 is a plan view schematically showing a relationship between thebattery pack mounted in the electric work vehicle and the rear wheels.

FIG. 4 is a side view of a riding electric mower, which is an example ofan electric work vehicle.

FIG. 5 is a plan view of the riding electric mower.

FIG. 6 is a schematic view showing a vehicle body frame, the batterypack, and a driving mechanism for a rear wheel unit.

FIG. 7 is a schematic view of the battery pack.

FIG. 8 is a view in vertical section of the battery pack.

FIG. 9 is an exploded view of a battery case.

FIG. 10 is a diagram showing a second embodiment (same through to FIG.16), and is a side view schematically showing a basic configuration ofan electric work vehicle in which a contactless charging system isincorporated.

FIG. 11 is a plan view schematically showing a basic configuration ofthe electric work vehicle in which the contactless charging system isincorporated.

FIG. 12 is a functional block diagram showing a basic configuration ofan electric circuit of the contactless charging system.

FIG. 13 is a side view of an electric mower.

FIG. 14 is a plan view of the electric mower.

FIG. 15 is a perspective view showing a support structure for thebattery pack, an electric motor unit, and a transmission in the vehiclebody frame.

FIG. 16 is a view in vertical section showing a region of the batterypack and the contactless charging system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the description hereinafter, unless explicitly described otherwise, a“vehicle body front-rear direction” is a direction of a vehicle bodycentral axis (also referred to as “vehicle body longitudinal axis”) thatextends in a horizontal direction along a travel direction of thevehicle body on which a battery pack is mounted. A “vehicle body lateraldirection” (also referred to simply as “lateral direction”) is adirection that extends in the horizontal direction, orthogonal to thevehicle body central axis. “Front (forward)” means on the forward sidein the vehicle body front-rear direction, and “rear (rearward)” means onthe reverse side in the vehicle body front-rear direction. “Left(leftward)” means left when facing the vehicle body forward direction,and “right (rightward)” means right when facing the vehicle body forwarddirection.

First Embodiment

Prior to describing specific embodiments of the battery pack relating tothe present invention, a basic structure of the battery pack mounted inthe electric work vehicle will be described with reference to FIG. 1,and a basic arrangement of the battery pack at the time of mounting sucha battery pack in the electric work vehicle will be described withreference to FIGS. 2 and 3.

A battery pack 6 as shown in FIG. 1 includes a battery case 60, ahorizontal partitioning wall 63, a battery electric unit 68 (a group ofelectric devices/accessories related to a battery; the collectivenomination will be simply referred to as “electric unit 68” also) andmultiple battery modules 6A. The battery case 60 is a sealed caseincluding a front case portion 61 and a rear case portion 62. Note thatin FIG. 1, the left side is defined as the front side (forward), and theright side is defined as the rear side (rearward). The front caseportion 61 and the rear case portion 62 are not individual members, butare respective nominations of a front-side portion and a rear-sideportion when considering the battery case 60 as being divided into afront-side portion and a rear-side portion. The battery case 60 isformed continuously by the front case portion 61 and the rear caseportion 62. In the example as shown in FIG. 1, a region of transitioningfrom the front case portion 61 to the rear case portion 62 is inclinedupward. Accordingly, the rear case portion 62 is shifted to the upperside relative to the front case portion 61 in the vertical direction,and the battery case 60 is a three-dimensional object having an upwardlevel difference in the middle. This level difference is required due torestrictions on site such as an installation space or the like.Therefore, the battery case 60 may have a downward level difference, orthere may be no level difference.

The horizontal partitioning wall 63 is a plate member that is providedso as to approximately divide the interior of the battery case 60 intotwo parts, namely an upper and a lower part. The interior of the frontcase portion 61 is divided in the up-down direction into a first spaceS1 and a second space S2 by the horizontal partitioning wall 63, and theinterior of the rear case portion is divided in the up-down directioninto a third space S3 and a fourth space S4 by the horizontalpartitioning wall 63. The first space S1 and the third space S3 are incommunication and form an upper portion space of the battery case.Similarly, the second space S2 and the fourth space S4 are incommunication and form a lower portion space of the battery case. Afront end gap G1 that allows air flow between the first space S1 and thesecond space S2 is formed between a front end 63 a of the horizontalpartitioning wall 63 and a wall surface in front of the horizontalpartitioning wall 63. A rear end gap G2 (FIG. 8) that allows air flowbetween the third space S3 and the fourth place S4 is formed between arear end 63 b of the horizontal partitioning wall 63 and a wall surfacebehind the horizontal partitioning wall 63. Accordingly, an aircirculation path is formed within the battery case 60 that extends fromthe first space S1, passes through the second space S2, the fourth spaceS4 and the third space S3, and returns to the first space S1.

In the example as shown in FIG. 1, the electric unit 68 is arranged inthe first space S1, and one battery module 6A is arranged in each one ofthe second space S2, the third space S3 and the fourth space S4. Thebattery module 6A is formed by a number of battery cells 6 a.Furthermore, a circulation fan 69 is arranged in the first space S1 soas to send air from the first space S1 to the third space S3.Accordingly, a flow path for circulated air is created, on which airpasses through the first space S1, the third space S3, the fourth spaceS4, the second space S2 and back to the first space S1 in the statedorder. The flow of the circulated air not only cools the electric unit68, but also uniformizes the temperatures of the second space S2, thethird space S3 and the fourth space S4, in which the battery modules 6Aare arranged. Accordingly, malfunction of the battery module 6A causedby non-uniformity in the temperature distribution is prevented.

The battery case 60 is configured to be at least partially removable orhas an opening formed therein to be closed by a lid, for the purpose ofmaintenance inspection of the electric unit 68 or the battery modules6A.

FIGS. 2 and 3 are a side view and a plan view, respectively, forillustrating a basic example of mounting the battery pack 6 as shown inFIG. 1 in the electric work vehicle. The electric work vehicle includesa vehicle body frame 20 that includes a left frame 21 and a right frame22 that extend in the vehicle body front-rear direction with an intervaltherebetween in the vehicle body lateral direction, and at least onecrossbeam 23 that connects the left frame 21 and the right frame 22. Aleft front wheel 11L and a right front wheel 11R that constitute a frontwheel unit are arranged at a front portion of the vehicle body frame 20.A left rear wheel 12L and a right rear wheel 12R that constitute a rearwheel unit are arranged on a rear side relative to the center of thevehicle body frame 20. Hereinafter, if there is no particular need tomake a distinction, the left front wheel 11L and the right front wheel11R will be referred to collectively as “front wheel unit 11”, and theleft rear wheel 12L and the right rear wheel 12R will be referred tocollectively as “rear wheel unit 12”. A rear axle center Pr extends in avehicle body lateral direction.

The battery pack 6 is arranged in a rear half region of the vehicle bodyframe 20 between the left frame 21 and the right frame 22. In a lateralside view, the front end of the battery pack 6 is located forward of therear axle center Pr and approximately near the front end of the rearwheel unit 12. The rear end of the battery pack 6 is locatedapproximately at the rear end of the vehicle body frame 20. As isapparent from FIG. 3, the battery pack 6 has a width sufficient tosnugly fit the battery pack 6 between the left frame 21 and the rightframe 22, and extends with an equal width in the vehicle body front-reardirection. Also, as is apparent from FIG. 2, the front half portion ofthe battery pack 6 is in the axle space of the rear wheel unit 12. As amore preferable mode of arranging the battery pack 6, the center ofgravity of the battery pack 6 is in the region between the front end andthe rear end of the rear wheel unit 12 on a center line in the vehiclebody front-rear direction. In other words, the center of gravity of thebattery pack 6 is within the distance of the rear wheel unit 12 from therear axle center Pr in the vehicle body front-rear direction.Accordingly, the weight of the battery pack 6 contributes to thestability (favorable balance) of the vehicle body.

Furthermore, the battery pack 6 has a shape in which the rear caseportion 62 is shifted to the upper side relative to the front caseportion 61 in the up-down direction. In other words, the battery pack 6has a three-dimensional shape constituted by a front-side rectangularcuboid portion 6F and a rear-side rectangular cuboid portion 6B, and therear-side rectangular cuboid portion 6B protrudes upward relative to thefront-side cuboid portion 6F. In other words, an upward level differenceis formed on the upper surface and the lower surface of the battery pack6.

Accordingly, an above-ground height Hb of the rear case portion 62 ofthe battery pack 6 is higher than an above-ground height Hf of the frontcase portion 61 of the battery pack 6. In the example as shown in FIG.2, the above-ground height Hf of the front case portion 61 isapproximately the same as the above-ground height of the lower end ofthe rear axle case 31 of the rear wheel unit 12. The above-ground heightHb of the rear case portion 62 of the battery pack 6 is higher than theabove-ground height of the rear axle case 31 and is approximately thesame as the above-ground height of the rear axle center Pr. The lowestabove-ground height of the vehicle body frame 20 at the portionsupporting the battery pack 6 approximately coincides with the lowestabove-ground height of the battery pack 6. Due to the above-groundheight Hf of the front case portion 61 being set to be lower, the centerof gravity of the battery pack 6 is lower, and travel stability is morepreferable. Also, due to the above-ground height Hb of the rear caseportion 62 being set to be higher, the rear end of the battery pack 6 orthe vehicle body frame 20 is less likely to collide with the groundsurface or stones during uphill travel or off-road travel.

The left motor 4L that transmits the rotational power to the left rearwheel 12L is arranged near the front case portion 61 of the battery packin the periphery of the left rear wheel 12L. The right motor 4R thattransmits the rotational power to the right rear wheel 12R is arrangednear the rear case portion 62 in the periphery of the right rear wheel12R.

The left motor 4L and the right motor 4R are arranged at left-rightsymmetrical positions. In order to create spaces for arranging the leftmotor 4L and the right motor 4R, the portion covering the first space S1of the front case portion 61 may be recessed. A driver seat 16 isarranged above the left motor 4L and the right motor 4R, and thus spaceis used effectively.

For further effective use of space, in the battery pack 6 illustrated inFIG. 1, the front-side rectangular cuboid portion 6F of the battery pack6 has a protruding central portion 6Fc that extends in the vehicle bodyfront-rear direction, with an upper right portion and an upper leftportion of the front-side rectangular cuboid portion 6F being removed.Due to this, spaces are created on the left and right of the centralportion 6Fc. The left motor 4L enters the space on the left side of thecentral portion 6Fc of the front-side rectangular cuboid portion 6F, andthe right motor 4R enters the space on the right side of the centralportion 6Fc.

Next, a specific example of an electric work vehicle on which a batterypack is mounted will be described. FIG. 4 is a side view of a ridingelectric mower, which is an example of an electric work vehicle, andFIG. 5 is a plan view of the riding electric mower.

As shown in FIGS. 4 and 5, the riding electric mower (hereinafterreferred to as simply “mower”) includes a vehicle body 10. The vehiclebody 10 is supported on the ground by a caster-type front wheel unit 11having a left front wheel 11L and a right front wheel 11R, and by a rearwheel unit 12 including a left rear wheel 12L and a right rear wheel 12Rwhich are rotatably driven. The vehicle body 10 has a vehicle body frame20 as a base frame. The vehicle body frame 20 includes a left frame 21,a right frame 22, and a crossbeam 23 that joins the left frame 21 andthe right frame 22. A mower unit 13 hangs down from the vehicle bodyframe 20 via a link mechanism 14 between the front wheel unit 11 and therear wheel unit 12. The mower unit 13 includes a blade transmissionmechanism 131 and a blade 132 rotated by the blade transmissionmechanism 131. A driver seat 16 is arranged in a central region in thevehicle body front-rear direction of the vehicle body 10. The basicstructure of the battery pack 6 and the basic arrangement of the vehiclebody frame 20 employ those described with reference to FIGS. 1 and 2.

FIG. 6 is a perspective view showing the vehicle body frame 20, thebattery pack 6 and the drive mechanism for the rear wheel unit 12. Thedrive mechanism that supplies the rotational power to the rear wheelunit 12 includes a motor 4, a transmission case 30 and the rear axlecase 31. As shown in FIG. 6, the left frame 21 and the right frame 22each branch vertically from an intermediate region and re-join in a rearregion. In other words, in the rear half region, the left frame 21includes an upper frame portion 21 a and a lower frame portion 21 b.Similarly, in the rear half region, the right frame 22 includes an upperframe portion 22 a and a lower frame portion 22 b. In a side view, aleft transmission case 30L is arranged in the region between the upperframe portion 21 a and the lower frame portion 21 b of the left frame21, and a right transmission case 30R is arranged in the region betweenthe upper frame portion 22 a and the lower frame portion 22 b of theright frame 22. A left rear axle case 31L is connected to the lefttransmission case 30L, and the left rear wheel 12L is supported by theleft rear axle case 31L. A right rear axle case 31R is connected to theright transmission case 30R, and the right rear wheel 12R is supportedby the right rear axle case 31R. The left rear axle case 31L is atubular member in which the left rear axle 41 of the left rear wheel 12Lis mounted, and which performs bearing support, and the outer shapethereof is a truncated cone shape. Similarly, the right rear axle case31R is a tubular member in which the right rear axle 42 of the rightrear wheel 12R is mounted, and which performs bearing support, and theouter shape thereof is a truncated cone shape. The battery pack 6 isarranged such that, in plan view, the center of gravity of the batterypack 6 is approximately located on a center line in the vehicle bodyfront-rear direction and is within the length of the rear wheel radiuson the front side and rear side from the rear axle center Pr.

The left transmission case 30L is a hollow member that extends forwardin the vehicle body front-rear direction from the left rear axle case31L orthogonally to the rear axle center Pr which acts also as thecentral axis center of the left rear axle case 31L, and the lefttransmission having a gear transmission mechanism is housed within theleft transmission case 30L. A surface for mounting the left motor 4L isformed on a power input portion 32 f of the left transmission case 30L.Similarly, the right transmission case 30R is a hollow member thatextends forward in the vehicle body front-rear direction from the rightrear axle case 31R orthogonally to the rear axle center Pr which actsalso as the central axis center of the right rear axle case 31R, and theright transmission having a gear transmission mechanism is housed withinthe right transmission case 30R. The gear transmission mechanismgenerally reduces the input power, but may increase the input power.Still alternatively, there may be provided a gear transmission mechanismthat does not increase and reduce the input power. A surface formounting the right motor 4R is formed on the power input portion 32 f ofthe right transmission. In this embodiment, the left transmission case30L and the left rear axle case 31L are formed integral, and the righttransmission case 30R and the right rear axle case 31R are formedintegral. Note that instead of the gear transmission mechanism, a chaintransmission mechanism, a transmission shaft mechanism or the like maybe used as the left transmission and the right transmission.

Speed changing operations on the left motor 4L and the right motor 4Rare performed using a left and right pair of speed changing levers 18(see FIGS. 4 and 5), which are arranged on both sides of the driver seat16. When a speed changing lever 18 is held at a front-rear neutralposition, the corresponding motor 4 enters a stopped state; and byoperating the speed changing lever 18 forward from the neutral position,the corresponding motor 4 performs driving so as to rotate normally andrealizes a forward speed change, and by operating the speed changinglever 18 rearward, the corresponding motor 4 performs driving so as torotate in reverse, thereby realizing a reverse speed change. Byindependently operating the left and right pair of speed changing levers18, the left motor 4L and the right motor 4R are independently subjectedto variable speed driving control. For example, when the left and rightpair of speed changing levers 18 are operated by approximately the sameoperation amount in the forward direction from the neutral position,both the left rear wheel 12L and the right rear wheel 12R are driven atapproximately the same speed, and the vehicle body 10 travels forwardlinearly. When the left and right pair of speed changing levers 18 areoperated by approximately the same operation amount in the rearwarddirection from the neutral position, the left rear wheel 12L and theright rear wheel 12R are driven in the reverse direction atapproximately the same speed, and the vehicle body 10 travels in reverselinearly. Furthermore, when the left and right pair of speed changinglevers 18 are operated by mutually different operation amounts, the leftrear wheel 12L and the right rear wheel 12R are driven at differentspeeds, and the vehicle body 10 turns. In such a case, a turn with asmall radius can be performed by setting one of the left rear wheel 12Land the right rear wheel 12R to a low speed close to zero and operatingthe other to the forward side or the reverse side at a high speed.Furthermore, by driving the left rear wheel 12L and the right rear wheel12R in mutually opposite directions, it is possible to cause the vehiclebody 10 to perform a spin turn using the approximate central portion ofthe rear wheel unit 12 as the turn center.

With reference to FIGS. 6, 7, 8 and 9, a detailed configuration of thebattery pack 6 will be described next. The battery pack 6 includesmultiple battery modules 6A accommodated in the battery case 60. In thedescription of the basic configuration of the battery pack 6 withreference to FIGS. 1, 2 and 3, the battery pack 6 is described as anintegral unit including the battery case 60 and the battery module 6A.The front half of the battery pack 6 is defined as the front-siderectangular cuboid portion 6F, and the rear half of the battery pack 6is defined as the rear-side rectangular cuboid portion 6B. Furthermore,the protruding central portion 6Fc is formed on the upper half of thefront-side rectangular cuboid portion 6F, the left motor 4L is arrangedin the space on the left side of the central portion 6Fc, and the rightmotor 4R is in the space on the right side of the central portion 6Fc.Such an arrangement structure is employed also in the presentembodiment. In the description of the battery pack 6 hereinafter,however, the structure of the battery case 60 and the structure of thebattery modules 6A, which are originally separate members, will bedescribed separately.

The battery case 60 is a molded product divided into an upper portionand a lower portion, forming an upper case 60 a and a lower case 60 b,respectively. However, in order to facilitate the description of theinternal structure, the battery case 60 will be described as beingdivided into a front case portion 61 and a rear case portion 62.

The front case portion 61 is a three-dimensional member with an upperportion on which the protruding central portion 611 is formed byrecessing the upper left portion and upper right portion of arectangular cuboid. In other words, on both sides in the vehicle bodylateral direction of the central portion 611, the length in the vehiclebody lateral direction is shorter to form motor-accommodating spacesthat allow the left motor 4L and the right motor 4R to enter,respectively. The rear case portion 62 is a rectangular cuboid connectedto the front case portion 61 in the front-rear direction. The front caseportion 61 and the rear case portion 62 are connected in an orientationin which the rear case portion 62 is shifted upward, and the batterycase 60 has a three-dimensional shape with a vertical level differencebetween the front side and the rear side. Note that the central portion611 has an enlarged portion 612 that is enlarged on the left and rightand upward in the region connecting the front case portion 61 and therear case portion 62, and the internal space of the enlarged portion 612is expanded.

The rear case portion 62 has a rectangular cuboid shape with the samelateral width (length in the vehicle body lateral direction) as thefront case portion 61. The rear case portion 62 is shifted upwardrelative to the front case portion 61, whereby the battery case 60 has alevel-difference three-dimensional shape with a level difference betweenthe front case portion 61 and the rear case portion 62.

As shown in FIGS. 8 and 9, the interior of the battery case 60 dividedinto the upper case 60 a and the lower case 60 b is provided with ahorizontal partitioning wall 63, which divides the interior into upperand lower spanning across the front case portion 61 and the rear caseportion 62. The interior of the front case portion 61 is divided intothe first space S1 on the upper side and the second space S2 on thelower side by the horizontal partitioning wall 63, and the interior ofthe rear case portion 62 is divided into the third space S3 on the upperside and the fourth space S4 on the lower side by the horizontalpartitioning wall 63. The horizontal partitioning wall 63 is a platemember that is formed through a bending process so as to have a verticallevel difference similar to that of the battery case 60; and the secondspace S2, the third space S3 and the fourth space S4 have approximatelythe same shape and volume. The width and height of the first space S1are smaller than those of the other spaces. A vertical partitioning wall64 is provided between the first space S1 and the third space S3.

Battery modules 6A of the same specification are accommodated in thesecond space S2, the third space S3 and the fourth space S4. As shown inFIG. 9, the battery module 6A is a rectangular cuboid whose height islower compared to its longitudinal dimension and lateral dimension. Amultiple of battery cells 6 a are accommodated in the interior of thebattery module 6A.

The first space S1 accommodates an electric unit 68 including a relay, afuse and the like which are provided on an electrical wire forinterconnecting the battery modules 6A and an external device. Acirculation fan 69, which suctions the air in the first space S1 andsends it to the third space S3, is mounted on the vertical partitioningwall 64. The electrical system for the circulation fan 69 isincorporated in the electric unit 68. A front end gap G1 is formedbetween a front end 63 a of the horizontal partitioning wall 63 and thefront case portion 61, and a rear end gap G2 is formed between a rearend 63 b of the horizontal partitioning wall 63 and the rear caseportion 62. Furthermore, the battery case 60 has a sealed constructionsuch that grass and waste are not taken into the interior space of thebattery case 60 from the outside, or such that air flow between theinterior space and the outside is suppressed. Accordingly, in theinterior of the battery case 60, a circulated air flow path (indicatedby the arrows in FIG. 8) is formed which starts from the circulation fan69, passes through the third space S3, the fourth space S4 and thesecond space S2 to reach the first space S1, and returns to thecirculation fan 69. The temperatures of the four spaces in the batterycase 60 are equalized by the circulated air that flows on the circulatedair flow path. Also, the electric unit 68 is cooled by such circulatedair. In order to improve the cooling effect, fins 60 f are provided onthe wall surface of the battery case 60, although this is shown onlypartially in the drawing. The fins 60 f can be formed on one or both ofthe inner wall surface and the outer wall surface of the battery case60.

The upper wall of the front case portion 61 is provided with an openingfor maintenance inspection of the electric unit 68, and is usuallyclosed by a lid 613.

As shown in FIG. 4, in the present embodiment, a work motor 4W thatprovides power to the mower unit 13 serving as the work apparatus isarranged on the rear portion of the mower unit 13, and the power fromthe work motor 4W is transmitted to the blade transmission mechanism 131via a belt. Instead of this, the work motor 4W can be arranged on thefront side of the battery pack 6. In such a case, a PTO shaft (powertakeoff shaft), including an output shaft and a relay shaft from thework motor 4W, extends forward in the vehicle body front-rear direction,whereby the power from the work motor 4W is transmitted to the bladetransmission mechanism 131 of the mower unit 13 via the PTO shaft.

Other Embodiments in the First Embodiment

(1) In the above-described embodiment, the battery electric unit 68 isaccommodated in the first space S1, but this is not limitative. Insteadthereof, the battery electric unit 68 may be accommodated in one of thesecond space S2, the third space S3 and the fourth space S4; and thebattery modules 6A may be accommodated each within the remainder (i.e.each of the others of the four spaces S1-S4).(2) In the above-described embodiment, a riding electric mower isillustrated as an example of the electric work vehicle in which thebattery pack is mounted, but this is not limitative. Instead thereof,the battery pack can also be mounted in another electric work vehicle,such as an electric rice transplanter, an electric tractor, etc.

Second Embodiment

A basic configuration of an electric work vehicle in which a contactlesscharging system is incorporated will be described with reference toFIGS. 10 and 11.

The electric work vehicle includes a vehicle body frame 20 that includesa left frame 21 and a right frame 22 that extend in the vehicle bodyfront-rear direction with an interval therebetween in the vehicle bodylateral direction, and at least one crossbeam 23 that connects the leftframe 21 and the right frame 22. A left front wheel 11L and a rightfront wheel 11R that constitute a front wheel unit 11 are arranged atthe front portion of the vehicle body frame 20. A left rear wheel 12Land a right rear wheel 12R that constitute a rear wheel unit 12 arearranged rearward of the center of the vehicle body frame 20.Hereinafter, if there is no particular need to make a distinction, theleft front wheel 11L and the right front wheel 11R will be referred tocollectively as “front wheel unit 11”, and the left rear wheel 12L andthe right rear wheel 12R will be referred to collectively as “rear wheelunit 12”. A rear axle center Pr extends in a vehicle body lateraldirection.

The battery pack 6 is arranged in a region in the rear half of thevehicle body frame 20 between the left frame 21 and the right frame 22,and in a lateral side view. The front end portion of the battery pack 6is located forward of the rear axle center Pr and approximately near thefront end of the rear wheel unit 12. The rear end of the battery pack 6is located approximately at the rear end of the vehicle body frame 20.As is apparent from FIG. 11, the battery pack 6 has a width sufficientto snugly fit the battery pack 6 between the left frame 21 and the rightframe 22 and extends with an equal width in the vehicle body front-reardirection. Also, the front half of the battery pack 6 enters the axlespace of the rear wheel unit 12. The battery pack 6 has a shape obtainedby cutting away a front-side upper portion region and a rear-side lowerportion region from an approximate rectangular cuboid, the cutawayrear-side lower portion region creates a flat rectangular cuboid-shapedrear recessed portion BS, and the cut away front-side upper portionregion creates a flat rectangular cuboid-shaped front recessed portionFS.

The motor 4, that drives the rear wheel unit 12, i.e. the drivingwheels, includes a left motor 4L that transmits rotational power to theleft rear wheel 12L, and a right motor 4R that transmits rotationalpower to the right rear wheel 12R. As shown in FIG. 11, the left motor4L enters the left side region of the front recessed portion FS. Theright motor 4R enters the right side region of the front recessedportion FS. The left motor 4L and the right motor 4R are arranged atpositions that are left-right symmetrical. The left motor 4L and theright rear axle case 31L are joined by a left transmission 130L, and theright motor 4R and the right rear axle case 31R are joined by a righttransmission 130R. The left transmission 130L is arranged on the outsideof the left frame 21, and the right transmission 130R is arranged on theoutside of the right frame 22. The left motor 4L and the right motor 4Rare collectively referred to as an “electric motor unit” as well. Theleft transmission 130L and the right transmission 130R are collectivelyreferred to as a “transmission 130”. The left rear axle case 31L and theright rear axle case 31R are collectively referred to as a “rear axlecase 31”. A driver seat 16 is arranged above the electric motor unit(motor 4), and thus the space is used effectively.

A contactless charging system, that charges the battery pack 6 withoutcoming into contact therewith, includes a primary coil unit 8 arrangedon a ground surface, and a secondary coil unit 7 attached to theelectric work vehicle. In the example as shown in FIG. 10, the primarycoil unit 8 has a two-stage structure, a coil power supply circuitportion 81 is arranged on the lower stage, a primary coil 80 is arrangedon the upper stage, and an elevation mechanism 8 a is provided betweenthe coil power supply circuit portion 81 and the primary coil 80. Theabove-ground height of the primary coil 80 can be adjusted using theelevation mechanism 8 a. A box-shaped housing 8 b accommodates the coilpower supply circuit portion 81, the primary coil 80 and the elevationmechanism 8 a; and the housing 8 b is provided with wheels 85 for movingthe primary coil unit 8, and stoppers 86 for holding a stopped positionof the primary coil unit 8. The secondary coil unit 7 includes asecondary coil 70 that electromagnetically couples with the primary coil80, and a charging circuit portion 71 that rectifies the power from thesecondary coil 70 and supplies the rectified power to the battery pack6. In the example as shown in FIG. 10, the secondary coil 70 and thecharging circuit portion 71 that constitute the secondary coil unit 7are not formed integral with each other, but the secondary coil 70 isarranged below the battery pack 6, and the charging circuit portion 71is arranged on the upper part of the battery pack 6. The secondary coil70 enters a rear recessed portion BS, which is a recessed portion formedin the lower portion of the battery pack 6, and the secondary coil 70 issupported by one or both of the battery pack 6 and the vehicle bodyframe 20 using a coil support member 79.

As shown in FIG. 12, the coil power supply circuit portion 81 of theprimary coil unit 8 includes a rectifying circuit 82, a communicationcontrol unit 83 and an inverter 84. The charging circuit portion 71 ofthe secondary coil unit 7 includes a rectifying circuit 72 and acommunication control unit 73. The rectifying circuit 82 is connected toa commercial power source via a power source cable to generate a DCvoltage, and provides the inverter 84 with the generated DC voltage. Theinverter 84 generates an alternating voltage using the input DC voltageand causes the alternating voltage to flow through the primary coil 80.The alternating voltage generated by the secondary coil 70 that iselectromagnetically coupled to the primary coil 80 is allowed to flowthrough the rectifying circuit 72 of the charging circuit portion 71,whereby a charging DC voltage with a predetermined voltage value isoutputted from the rectifying circuit 72. The rectifying circuit 72 isconnected to the battery pack 6, and a charging current is supplied tothe battery pack 6 using the charging DC voltage.

The communication control unit 83 of the coil power supply circuitportion 81 and the communication control unit 73 of the charging circuitportion 71 can exchange information through wireless communication.During the charging of the battery pack 6, charging information isexchanged to control the coil power supply circuit portion 81 and thecharging circuit portion 71. A notifying device (a buzzer 91, a lamp 92,or the like, see FIG. 10), that notifies a driver or an operator thatthe primary coil 80 and the secondary coil 70 are at appropriatepositions, is included in one or both of the coil power supply circuitportion 81 and the charging circuit portion 71.

Note that the battery pack 6 is connected to a power drive unit 5serving as an output destination. A motor control unit 50 and aninverter 51 are included in the power drive unit 5, and a motor drivecurrent, which is outputted from the inverter 51 based on a controlsignal from the motor control unit 50, is sent to the left motor 4L andthe right motor 4R.

One specific embodiment of the electric work vehicle will be describednext with reference to the drawings. FIG. 13 is a side view of amid-mount electric mower, which is an example of an electric workvehicle, and FIG. 14 is a plan view of the mid-mount electric mower. Theelectric mower (hereinafter referred to simply as “mower”) employs thecontactless charging system as described above with reference to FIGS.10, 11 and 12.

As shown in FIGS. 13 and 14, the mower includes the vehicle body 10. Thevehicle body 10 is supported on the ground by a caster-type front wheelunit 11 including a left front wheel 11L and a right front wheel 11R,and by a rear wheel unit 12 including a left rear wheel 12L and a rightrear wheel 12R which are rotatably driven. The vehicle body 10 has avehicle body frame 20 as a base frame. The vehicle body frame 20includes the left frame 21, the right frame 22, and the crossbeam 23that joins the left frame 21 and the right frame 22. A mower unit 13hangs down from the vehicle body frame 20 via a link mechanism 14between the front wheel unit 11 and the rear wheel unit 12. The mowerunit 13 includes a blade transmission mechanism 131 and blades 132 thatare rotated by the blade transmission mechanism 131. A driver seat 16 isarranged in a central region in the vehicle body front-rear direction ofthe vehicle body 10.

As shown in FIG. 15, the left frame 21 and the right frame 22 eachbranch vertically from a front/rear central region and rejoin in a rearregion in the front-rear direction. In more particular, the left frame21 includes an upper frame portion 21 a and a lower frame portion 21 bin the rear half region thereof. Similarly, the right frame 22 includesan upper frame portion 22 a and a lower frame portion 22 b in the rearhalf region thereof. In a lateral side view, a left transmission 130L isarranged in the region between the upper frame portion 21 a and thelower frame portion 21 b of the left frame 21, and a right transmission130R is arranged in the region between the upper frame portion 22 a andthe lower frame portion 22 b of the right frame 22. A left rear axlecase 31L is connected to the left transmission 130L, and the left rearwheel 12L is supported by the left rear axle case 31L. A right rear axlecase 31R is connected to the right transmission 130R, and the right rearwheel 12R is supported by the right rear axle case 31R. The left rearaxle case 31L is a tubular member in which the left rear axle 41 of theleft rear wheel 12L is mounted, and which performs bearing support, andthe outer shape thereof is a truncated cone shape. Similarly, the rightrear axle case 31R is a tubular member in which the right rear axle 42of the right rear wheel 12R is mounted, and which performs bearingsupport, and the outer shape thereof is a truncated cone shape. Thebattery pack 6 is arranged such that, in plan view, the center ofgravity of the battery pack 6 is approximately located on the centerline in the vehicle body front-rear direction and falls within thelength of the rear wheel radius on the front side and rear side from therear axle center Pr.

The left transmission 130L includes a gear transmission mechanism andextends forward in the vehicle body front-rear direction orthogonally tothe rear axle center Pr, which acts also as the central axle center ofthe left rear axle case 31L. The left transmission 130L and the leftrear axle case 31L are formed integral, and the left motor 4L is joinedto the input portion of the left transmission 130L. Similarly, the righttransmission 130R includes a gear transmission mechanism, and extendsforward in the vehicle body front-rear direction so as to be orthogonalto the rear axle center Pr, which acts also as the central axis centerof the right rear axle case 31R. The right transmission 130R and theright rear axle case 31R are formed integral, and the right motor 4R isjoined to the input portion of the right transmission 130R.

Speed changing operations on the left motor 4L and the right motor 4Rare performed using a left and right pair of speed changing levers 18(see FIGS. 12 and 13), which are arranged on both sides of the driverseat 16. When a speed changing lever 18 is held at a front-rear neutralposition, the corresponding left motor 4L or right motor 4R enters thestopped state. By operating the speed changing lever 18 forward from theneutral position, the left motor 4L or right motor 4R performs forwarddriving and forward speed change is realized, and by operating the speedchanging lever 18 rearward, the left motor 4L or right motor 4R performsreverse driving and reverse speed change is realized. By independentlyoperating the left and right pair of speed changing levers 18, the leftmotor 4L and the right motor 4R can independently perform variable speeddriving.

As shown in FIGS. 15 and 16, the battery pack 6 includes multiplebattery modules 6A accommodated in the battery case 60. The battery case60 is a molded product divided into an upper and lower portion, andincludes an upper case 60 a and a lower case 60 b. Hereinafter, thefront half of the battery case 60 is referred to as a front case portion61, and the rear half of the battery case 60 is referred to as a rearcase portion 62.

The rear case portion 62 is shifted upward relative to the front caseportion 61, whereby the battery case 60 has a level-difference cubicshape with a level difference between the front case portion 61 and therear case portion 62.

As shown in FIG. 16, the interior of the battery case 60 divided intothe upper case 60 a and the lower case 60 b is provided with thehorizontal partitioning wall 63, which vertically divides the interiorinto two portions spanning across the front case portion 61 and the rearcase portion 62. The interior of the front case portion 61 is dividedinto the first space S1 on the upper side and the second space S2 on thelower side by the horizontal partitioning wall 63, and the interior ofthe rear case portion 62 is divided into the third space S3 on the upperside and the fourth space S4 on the lower side by the horizontalpartitioning wall 63. The horizontal partitioning wall 63 is a platemember that is formed through a bending process so as to have a verticallevel difference similar to that of the battery case 60, and the secondspace S2, the third space S3 and the fourth space S4 have approximatelythe same shape and volume. The width and height of the first space S1are smaller than those of the other spaces. A vertical partitioning wall64 is provided between the first space S1 and the third space S3.

The electric unit 68 is accommodated in the first space S1. Batterymodules 6A of the same specification are accommodated in the secondspace S2, the third space S3, and the fourth space S4. A multiple ofbattery cells 6 a are accommodated in the interior of the battery module6A.

The first space S1 accommodates an electric unit 68 having a relay, afuse and the like provided on an electrical wire for connecting thebattery module 6A with an external device. The circulation fan 69, whichsuctions the air in the first space S1 and sends it to the third spaceS3, is mounted on the vertical partitioning wall 64. The electricalsystem for the circulation fan 69 is incorporated in the electric unit68. Accordingly, in the interior of the battery case 60, a circulatedair flow path (indicated by the arrows in FIG. 16) is formed whichstarts from the circulation fan 69, passes through the third space S3,the fourth space S4 and the second space S2 to reach the first space S1,and returns to the circulation fan 69. The temperatures of the fourspaces in the battery case 60 are equalized by the circulated air thatflows on the circulated air flow path.

As shown in FIG. 16, the secondary coil 70 is held by the coil supportmember 79 so as to oppose the lower surface of the lower case 60 b ofthe battery pack 6. The coil support member 79 is fixed to the vehiclebody frame 20 via a crossbar that joins the lower frame portion 21 b ofthe left frame 21 and the lower frame portion 22 b of the right frame22. The secondary coil 70 is arranged between the lower frame portion 21b on the left side and the lower frame portion 22 b on the right side inan orientation in which the magnetic force lines thereof are oriented inthe vertical direction, and therefore the lower frame portion 21 b andthe lower frame portion 22 b on the right side form a protection fencein the vehicle body lateral direction.

The primary coil unit 8 is moved so that the primary coil 80 is locateddirectly below the secondary coil 70. In such a case, adjustment of theposition in the vehicle body lateral direction can be performed bymoving the primary coil unit 8, and adjustment of the position in thevehicle body front-rear direction can be performed by slightly movingthe mower forward or in reverse. The buzzer 91 and lamp 92 serving asthe notifying devices that perform reporting when the primary coil 80and the secondary coil 70 are in the correct positional relationship(when the correct power is transmitted) are attached to the coil supportmember 79. A similar notifying device may be provided on the primarycoil unit 8. Furthermore, in order to align the primary coil 80 with thesecondary coil 70 by operating the mower, a lamp on an operation panelmay be used for a notifying device as well.

Other Embodiments in the Second Embodiment

(1) In the above-described embodiment, the primary coil 80 and the coilpower supply circuit portion 81 of the primary coil unit 8 are arrangedin two, upper and lower stages.

Instead thereof, the primary coil 80 and the coil power supply circuitportion 81 may be arranged laterally side by side.

(2) In the above-described embodiment, the secondary coil unit 7 isdivided into the secondary coil 70 and the charging circuit portion 71and arranged at the lower portion and the upper portion of the batterypack 6, respectively. Instead thereof, the secondary coil 70 and thecharging circuit portion 71 may be formed integral with each other andarranged below the battery pack 6.

(3) In the above-described embodiment, a mid-mount electric mower isgiven as an example of an electric work vehicle in which a contactlesscharging system of the present invention is incorporated. Insteadthereof, a contactless charging system of the present invention can alsobe applied to a front-mount electric mower, an agricultural work machinesuch as a rice transplanter, a combine-harvester and tractor, aconstruction machine such as a backhoe and a bucket loader or the like.

What is claimed is:
 1. An electric work vehicle battery pack,comprising: a sealed battery case including a front case portion and arear case portion; a horizontal partitioning wall that divides aninterior of the front case portion into a first space and a second spacein a vertical direction, and divides an interior of the rear caseportion into a third space and a fourth space in the vertical direction;a battery electric unit accommodated in one of the first space, thesecond space, the third space and the fourth space; and a battery moduleaccommodated in each of the remaining spaces among the first space, thesecond space, the third space and the fourth space.
 2. The electric workvehicle battery pack according to claim 1, further comprising acirculation fan configured to create a circulated air flow thatcirculates through the first space, the second space, the third spaceand the fourth space.
 3. The electric work vehicle battery packaccording to claim 2, wherein the circulation fan is accommodated in thesame space as the battery electric unit.
 4. The electric work vehiclebattery pack according to claim 1, wherein the rear case portion isshifted upward relative to the front case portion, and the battery casehas a level-difference three-dimensional shape in which a leveldifference is formed between the front case portion and the rear caseportion.
 5. The electric work vehicle battery pack according to claim 1,wherein the battery case is provided with an opening through which thebattery electric unit is exposed to the outside and which is closed by alid.
 6. The electric work vehicle battery pack according to claim 1,wherein a cooling fin is formed on a wall surface of the battery case.7. An electric work vehicle, comprising: a battery pack mounted on avehicle body; a left frame and a right frame that extend in a vehiclebody front-rear direction with an interval therebetween in a vehiclebody lateral direction; and a rear wheel unit having a left rear wheelthat is arranged outside in the vehicle body lateral direction of theleft frame, and a right rear wheel that is arranged outside in thevehicle body lateral direction of the right frame, wherein the batterypack comprises: a sealed battery case including a front case portion anda rear case portion; a horizontal partitioning wall that divides aninterior of the front case portion into a first space and a second spacein a vertical direction, and divides an interior of the rear caseportion into a third space and a fourth space in the vertical direction;a battery electric unit accommodated in one of the first space, thesecond space, the third space and the fourth space; and a battery moduleaccommodated in each of the remaining spaces among the first space, thesecond space, the third space and the fourth space, and a front end ofthe battery pack is arranged between the left rear wheel and the rightrear wheel so as to be located forward of an axle center of the rearwheel unit.
 8. An electric work vehicle, comprising: a left frame and aright frame that extend in a vehicle body front-rear direction with aninterval therebetween in a vehicle body lateral direction; a rear wheelunit having a left rear wheel arranged outside of the left frame in thevehicle body lateral direction and a right rear wheel arranged outsideof the right frame in the vehicle body lateral direction; a battery packarranged between the left rear wheel and the right rear wheel, a frontend of the battery pack being located forward of an axle center of therear wheel unit in the vehicle body front-rear direction; a left motorthat is arranged above the battery pack in the periphery of the leftrear wheel and is configured to receive a supply of power from thebattery pack and transmit rotational power to the left rear wheel; and aright motor that is arranged above the battery pack in the periphery ofthe right rear wheel and is configured to receive a supply of power fromthe battery pack and transmit rotational power to the right rear wheel.9. The electric work vehicle according to claim 8, wherein in a planview, a center of gravity of the battery pack is located in a rear wheelsegment defined by the left rear wheel and the right rear wheel in thevehicle body front-rear direction and the vehicle body lateraldirection.
 10. The electric work vehicle according to claim 8, whereinthe battery pack includes a front-side rectangular cuboid portion and arear-side rectangular cuboid portion shifted upward relative to thefront-side rectangular cuboid portion, and has a level-differencethree-dimensional shape having level differences on an upper surface anda lower surface of the battery pack between the front-side rectangularcuboid portion and the rear-side rectangular cuboid portion.
 11. Theelectric work vehicle according to claim 8, further comprising a rearaxle case through which the axle center of the rear wheel unit passes inthe vehicle lateral direction, wherein a rear end of the battery pack islocated rearward of the rear wheel unit in the vehicle body front-reardirection, and an above-ground height of the rear end of the batterypack is higher than an above-ground height of the rear axle case. 12.The electric work vehicle according to claim 8, further comprising afront wheel unit including a left front wheel that is arranged on anouter side of the left frame in the vehicle body lateral direction, anda right front wheel that is arranged on an outer side of the right framein the vehicle body lateral direction, wherein a mower unit is arrangedbetween the front wheel unit and the rear wheel unit.
 13. The electricwork vehicle according to claim 12, further comprising a work motorconfigured to supply power to the mower unit, the work motor beingarranged on a front side with respect to the front end of the batterypack in the vehicle body front-rear direction.
 14. The electric workvehicle according to claim 8, wherein a left transmission case isarranged on an outer side of the left frame in the vehicle body lateraldirection, the left transmission case accommodating a left transmissionconfigured to transmit rotational power from an output shaft of the leftmotor to an axle of the left rear wheel, and a right transmission caseis arranged on an outer side of the right frame in the vehicle bodylateral direction, the right transmission case accommodating a righttransmission configured to transmit rotational power from an outputshaft of the right motor to an axle of the right rear wheel.
 15. Theelectric work vehicle according to claim 14, wherein the lefttransmission case is joined to the left frame along the vehicle bodyfront-rear direction, and the right transmission case is joined to theright frame along the vehicle body front-rear direction.
 16. Acontactless charging system for an electric work vehicle, comprising: aprimary coil unit that includes a coil power supply circuit portion anda primary coil arranged above the coil power supply circuit portion, theprimary coil unit being arranged on a ground surface; a battery packarranged at a rear portion of a vehicle body frame, between a left andright pair of rear wheels; a secondary coil that electromagneticallycouples with the primary coil; a charging circuit portion configured torectify power from the secondary coil and supply the rectified power tothe battery pack; and a coil support member for arranging the secondarycoil below the battery pack.
 17. The contactless charging systemaccording to claim 16, wherein the charging circuit portion is attachedto an upper portion of the battery pack.
 18. The contactless chargingsystem according to claim 16, wherein a recessed portion is formed at arear-side lower portion of the battery pack and the secondary coil isarranged in the recessed portion.
 19. The contactless charging systemaccording to claim 16, wherein the primary coil unit is provided with anelevation mechanism configured to raise and lower the primary coil. 20.An electric mower in which a contactless charging system isincorporated, wherein the contactless charging system comprises: aprimary coil unit that includes a coil power supply circuit portion anda primary coil arranged above the coil power supply circuit portion, theprimary coil unit being arranged on a ground surface; a battery packarranged at a rear portion of a vehicle body frame, between a left andright pair of rear wheels; a secondary coil that electromagneticallycouples with the primary coil; a charging circuit portion configured torectify power from the secondary coil and supply the rectified power tothe battery pack; and a coil support member for arranging the secondarycoil below the battery pack, a mower unit hangs down elevatably at afront portion of the vehicle body frame, and an electric motor unitconfigured to drive the rear wheels using power supplied from thebattery pack via a motor power supply circuit portion is arrangedforward of an axle center of the rear wheels, between the rear wheels.21. The electric mower according to claim 20, wherein the electric motorunit includes a left motor that drives one rear wheel via a lefttransmission, and a right motor that drives the other rear wheel via aright transmission, the left motor and the left transmission beingarranged between the one rear wheel and the battery pack, and the rightmotor and the right transmission being arranged between the other rearwheel and the battery pack.
 22. The electric mower according to claim21, wherein a lower surface of the mower unit at the highest position islower than a lower surface of the secondary coil.